Electrochemical Synthesis of Individual Core@Shell and Hollow Ag/Ag<sub>2</sub>S Nanoparticles Donald A. Robinson Henry S. White 10.1021/acs.nanolett.9b02144.s001 https://acs.figshare.com/articles/journal_contribution/Electrochemical_Synthesis_of_Individual_Core_Shell_and_Hollow_Ag_Ag_sub_2_sub_S_Nanoparticles/9118421 This letter presents an electrochemical methodology for structure-tunable synthesis, characterization, and kinetic monitoring of metal–semiconductor phase transformations at individual Ag nanoparticles. In the presence of HS<sup>–</sup> in aqueous solution, the stochastic collision and adsorption of Ag nanoparticles at a Au microelectrode initiates the partial anodic transformation of Ag to Ag<sub>2</sub>S at each particle. A single continuous current transient is observed for each Ag nanoparticle reacted. The characteristic shapes of the transients are distinct from previously reported amperometric recordings of electrochemical reactions involving single nanoparticles and are highly uniform at a constant applied potential. The average maximum current increases while the event duration decreases as a function of increasing potential. Independent of applied potential, the electrochemical transformation event abruptly stops after converting ∼80% of the Ag in the nanoparticle to Ag<sub>2</sub>S, a self-terminating process that does not occur for bulk Ag electrodes under similar conditions. The resulting products are a mixture of core@shell Ag@Ag<sub>2</sub>S nanoparticles with and without voids in the core, as characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). Both the frequency and size of voids increase at more positive potentials. The average size of the core@shell nanoparticles determined by coulometric analysis of the current transients agrees well with TEM measurements. 2019-07-26 18:38:01 bulk Ag electrodes energy-dispersive X-ray spectroscopy Ag nanoparticles electrochemical transformation event HS event duration decreases TEM transmission electron microscopy EDX Ag 2 S